1. Field of the Invention
The invention relates to an anti-oxidative agent for molten metal, a method of preparing the same, and use thereof.
2. Description of the Related Art
In industrial production, it is common to melt a metal or an alloy so as to bind to or attach to another. However, most metals will be oxidized at presence of oxygen, such as the formation of iron rust. At high temperature, particularly at molten state, the oxidation of the metal or the alloy is very intense, resulting in oxide accumulation. Furthermore, in order to attach to another metal, the molten metal should flow circularly, which, on the one hand, accelerates the oxidation, on the other hand, brings the oxides and oxygen into the inside of the liquid metal. Thus, the oxidation further occurs inside the liquid metal and more and more metal dross containing the metal is produced, emerges, and accumulates. The metal dross inhibits the flow of the liquid metal or even overflows, which is dangerous and contaminates the equipment. Additionally, the metal dross cannot attach to metals and thereby must be removed. After removal of the metal dross, the height of the liquid metal surface decreases, the materials are not sufficient, so the addition of extra metal is required.
Therefore, in order to prevent the oxidation of the molten metal, anti-oxidative treatment is required. Conventional methods for anti-oxidation include reducing with a reductant, reducing with a reduction machine, and oxidation prevention with nitrogen, among which reducing with a reductant is common The practical reductants include a reducing powder, a reducing metal, and a viscous colloidal agent.
The working mode of the reducing powder is to apply the powder to the surface of the liquid metal, but the method has the following disadvantages:                a) powdery reductant is inconvenient in practice, particularly for a molten metal having a large surface area, it is not easy to spray uniformly;        b) powdery reductant is prone to be easily ejected away from the molten metal, resulting in pollution and material waste;        c) powdery agents are generally acids, bases, or salts which will react with additives upon mixing with the molten metal, resulting in a large amount of smoke, which is very difficult to remove with conventional ventilation systems; and        d) as mentioned above, powdery agents are generally acids, bases, or salts, which do a great harm to human, equipment, and environment.        
The working protocol for reducing a metal includes adding high purity of active substance (for example, a reducing powder) to a metal, cooling, preparing metal particle (or metal section), and adding the metal particle to a molten metal, but the method has the following disadvantages:                a) the preparation of reducing metal involves in a complicated process, resulting in a high cost;        b) prior to use, the reducing metal needs melting, which takes a long time, and the molten reducing metal is not easy to spread;        c) the alloy having the reducing metal is not absolutely the same as the target alloy to be protected, so the addition of the alloy having the reducing metal may destroy the metal proportion of the target alloy; and        d) the addition amount of the reducing metal should be accurate, which is difficult to control; excess reducing metal results in waste, increases the tension of the molten alloy, and decreases the adhesion.        
The working mode of the viscous colloidal agent includes adding an active substance to a viscous liquid, mixing, adding the mixture to a molten metal, and stirring so as to spread on the surface to form a protective membrane, but the method has the following disadvantages:                a) the spread is slow and needs strong stirring; and        b) the viscous colloidal agent has strong adhesion and is prone to adhere to the molten metal and the equipment, resulting in contamination, blocking, and destruction.        